The present invention relates to temperature probes used to monitor temperatures of turbine engines and specifically to a temperatures probe buffer amplifier to provide continuous compensation for thermally induced changes in the resistances of wiring connected to the temperature probe.
Modern engine control systems have temperature probe circuits which are subject to changes in the electrical resistance of its wiring induced by changes of temperature. While certain Resistance Temperature Device (RTD) probes have precisely known responses to changes in temperature, the usefulness of such probes is frustrated since the wires connected to the probes are also subject to changes in electrical characteristics caused by changes in temperature. What is needed is a means or circuit which will allow the use of such RTD probes, yet enable the probe to be responsive to changes in temperature while the host circuit connected to the probe remains in some manner immune to the effects of heat.
This task has been alleviated to some degree by prior art techniques that are designed to provide ambient temperature compensation features. The extent of these prior art techniques is given by the following patents:
U.S. Pat. No. 3,792,366 issued to Jornod on Feb. 12, 1974 PA0 U.S. Pat. No. 3,940,707 issued to Fernandez on Feb. 24, 1976 PA0 U.S. Pat. No. 4,185,251 issued to Brown, Jr. et al on Jan. 22, 1980 PA0 U.S. Pat. No. 4,218,613 issued to Bletz on Aug. 19, 1980 and PA0 U.S. Pat. No. 4,349,788 issued to Shaw et al on April 20, 1982.
While the above patents are instructive as to temperature compensation techniques, the specific devices they disclose are unsuitable to all needs. The Brown et al, Bletz and Fernandez devices comensate for voltage variations of automatic gain control (AGC) devices in which the internal circuitry of the AGC is affected by changes in temperature. In the present case, it is desirable that the RTD probe experience changes in electrical characteristics with changes of temperature: it is just the external circuitry connected to it which requires a means of temperature compensation. The Jornod and Shaw inventions provide for temperature compensation, but requires different adjustments and settings to be made to elements of the circuit Jornod and Shaw et al circuits, which include temperature sensitive resistors or thermistors in the input circuits of operational amplifiers, are unnecessary complex, and are not automatic in that they require adjustments.
In view of the foregoing, it is apparent that there currently exists the need for a device which automatically compensates for the thermal effects of external wiring of a temperature probe without any further adjustments being required. The present invention is directed towards satisfying that need.